There has been a rapid growth in recent years in the prevalence and variety of techniques for the desorption and ionization of sample species from solid surfaces at ambient atmospheric conditions, without significant sample preparation, followed by chemical analysis by mass spectrometry. Examples of such techniques include, but are not limited to: “desorption electrospray ionization” (DESI); “thermal desorption atmospheric pressure chemical ionization” (TD/APCI); “direct analysis in real time” (DART); “desorption atmospheric pressure chemical ionization” (DAPCI); and “laser desorption/electrospray ionization” (LD/ESI). Recent reviews that enumerate and elucidate such techniques are provided by: Van Berkel G J, et. al., “Established and emerging atmospheric pressure surface sampling/ionization techniques for mass spectrometry”, J. Mass Spectrom. 2008, 43, 1161-1180; and, Venter A., et al., “Ambient desorption ionization mass spectrometry”, Trends in Analytical Chemistry, 2008, 27, 284-290.
Most such techniques have been demonstrated with ion source configurations that were open to the environment. Open configurations are attractive because they can allow easy optimization of analysis conditions, such as sample positioning and reagent source positioning, easy sample treatment during analysis, such as heating or cooling, and a straightforward exchange of samples. However, open ion source configurations may exhibit serious deficiencies with respect to safety concerns which preclude their use in unregulated facilities, and are inadvisable elsewhere for the same reasons. For example, open source configurations may not provide adequate protection for the operator from accidental exposure to the high voltages and/or elevated temperatures typically employed in such sources. Open sources may also fail to contain vaporized sample and reagent material which is often very toxic.
Apart from such safety concerns, ion sources operating at atmospheric pressure often rely on chemical reactions involving gaseous species that are present naturally in the local ambient, such as water vapor, oxygen, and/or nitrogen. As such, the performance of such sources may vary significantly as the local concentration of such reactants drifts uncontrollably, resulting in degraded performance and/or poor reproducibility. There is a significant need for a direct sample analysis system that provides real-time monitoring, feedback, conditioning and control of sample background and ionization conditions.
To date, only a few attempts are known to have been made to configure such atmospheric pressure ion sources with an enclosure that provides for safe operation, and the ability to better control and manipulate the ambient environment. However, such attempts to outfit ambient atmosphere ion sources with an enclosure have at the same time compromised some of the more advantageous features of open ion sources, such as: the ability to readily optimize the position of samples, as well as the positions of various desorption and/or ionization components, for maximum ionization efficiency and transport of ions into vacuum during operation; to readily access a sample surface, for example, to monitor the surface temperature, or to visualize the surface appearance; and the ability to configure mechanisms that allow multiple samples to be loaded into a source at the same time; and, hence, to provide for the possibility of automated operation. Therefore, there has been a need for ambient pressure ion sources that are configured with an enclosure that provides operator protection and ambient environment control, while also providing for these advantageous features otherwise available with open ambient ion sources.
Additionally, prior ambient atmosphere ion sources have been configured to accommodate only a single type of solid, liquid, or gaseous samples. Hence, there is a need for an ambient atmosphere ion source that is able to accommodate one or more samples of one or more sample types in a relatively compact space, without requiring substantial reconfiguration or operator intervention. Furthermore, there has been a need for enclosed ambient atmosphere ion sources that provide automated identification and automated optimization of the position, and orientation of samples and auxiliary components, such as desorption and/or ionization probes.